Industrially synthesized single-walled carbon nanotubes: compositional data for users,environmental risk assessments, and source apportionment

Abstract

Commercially available single-walled carbon nanotubes (SWCNTs) contain largepercentages of metal and carbonaceous impurities. These fractions influence the SWCNTphysical properties and performance, yet their chemical compositions are not well defined.This lack of information also precludes accurate environmental risk assessments forspecific SWCNT stocks, which emerging local legislation requires of nanomaterialmanufacturers. To address these needs, we measured the elemental, molecular, and stablecarbon isotope compositions of commercially available SWCNTs. As expected,catalytic metals occurred at per cent levels (1.3–29%), but purified materialsalso contained unexpected metals (e.g., Cu, Pb at 0.1–0.3 ppt). Nitrogen contents(up to 0.48%) were typically greater in arc-produced SWCNTs than in thosederived from chemical vapor deposition. Toluene-extractable materials contributedless than 5% of the total mass of the SWCNTs. Internal standard losses duringdichloromethane extractions suggested that metals are available for reductivedehalogenation reactions, ultimately resulting in the degradation of aromaticinternal standards. The carbon isotope content of the extracted material suggestedthat SWCNTs acquired much of their carbonaceous contamination from theirstorage environment. Some of the SWCNTs, themselves, were highly depleted in13C relative to petroleum-derived chemicals. The distinct carbon isotopic signatures and uniquemetal ‘fingerprints’ may be useful as environmental tracers allowing assessment of SWCNTsources to the environment.